This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Few magnetic resonance (MR) studies have investigated possible structural alterations of the prefrontal cortex in individuals with obsessive-compulsive disorder (OCD) despite the importance of this region to neurobiologic models of the disorder. Assessment of frontal subregions in OCD is potentially important because it is known that the frontal lobes are both structurally and functionally heterogeneous. In this study we will use methods for cortical surface mapping to investigate the orbital frontal cortex, which has been implicated in the pathophysiology of OCD from functional neuroimaging studies. Twenty-five patients with a DSM-IV diagnosis of OCD and matched healthy volunteers will receive MR imaging scans consisting of 124 contiguous T1-weighted coronal SPGR MR images (slice thickness = 1.5mm). It is hypothesized that compared to healthy volunteers, patients will demonstrate increased grey matter density in the orbital frontal region consistent with functional neuroimaging studies demonstrating hypermetabolism of this region during rest conditions and symptom provocation. Increased grey matter density will be associated with worse neuropsychological functioning on measures of response inhibition. It is expected that these data will yield important information regarding the potential role of frontal cortical abnormalities in the neurobiology of OCD as well as abnormal structure-function relations.